Re: Evolution = gradual




Op 05-01-2008 19:49, in artikel 4Nudnf74x_OnTOLanZ2dnUVZ_q6mnZ2d@xxxxxxx, Cj
<Cj@xxxxxxxx> schreef:

"Aardvark J. Bandersnatch, BA, MA, BLT, PhD, MYOB, STFU"
<someone@xxxxxxxxxxxxx> wrote in message
news:cOudnTcCFNNz7eTanZ2dnUVZ_s2tnZ2d@xxxxxxxxxxxxxxxx

"Marc Verhaegen" <m_verhaegen@xxxxxxxxx> wrote in message
news:C39B14E5.B3C3%m_verhaegen@xxxxxxxxxxxx
Natura non facit saltum, Darwin said. Every evolutionary step is small &
every evolutionary phase has to be viable.

natura non facit saltus


If you'll pardon the correction.



Darwin didn't say it first...
If Marc will pardon the correction.

Of course.

One of the problems of the open plains hypotheses is that they're
discontinuous:
The original ?open plain¹ ideas were obviously hypothetical, but soon the
general impression of human ancestors coming out of the trees and colonizing
the vast plains became set in the minds of most palaeoanthropologists, and
different ideas ­ some more improbable than others ­ were put forward to
explain how savannah-dwelling ancestors might have found enough food and
water to survive on the open plains ­ as if the hypothesis had already been
proven. Human characteristics were discussed in an evolutionary setting that
involved a movement from the forests to the open plains, and reasons for
these characteristics always tended to revolve around the ?open plain¹ theme
(see Table 2). Even the most far-fetched of these ideas (for example, honey
collection, liver consumption, or food collection at noon on open plains)
have been seriously considered and published in scientific journals. Such ad
hoc explanations are comparable to the hypothetical ?land bridges¹ between
Africa and South-America that were popular in geology before the theory of
Plate Tectonics became accepted.
What is striking about these hypotheses is their combined diversity. Some
rely on hunting large game, others on small game, some on scavenging bone
marrow, or brains, or livers, or collecting seeds, or tubers, or honey. Some
of these ?open plain¹ models are more typical of slow-moving animals
(feeding on belowground resources), others of fast-moving mammals (³bouts of
strenuous activity²), and others rely on endurance (following migrating
ungulates, or the dogged pursuit of prey). This diversity of theoretical
models shows that the ?open plain¹ scenarios are not the result of usual
biological thinking. In evolutionary biology, hypotheses are not just
?possible scenarios¹, but normally the result of solid analyses of
relationships between form and function. Biologists usually do not propose a
scenario to explain the evolution of an animal without a careful comparison
of different features of this animal with similar features (convergences) of
other, not closely related species.
Whereas modern biology sees evolution as a sequence of overlapping niches
(Kemp 2007), the proposed lifestyles of these early human ancestors are
discontinuous and have little or no overlap. Frequently they are
incompatible with each other. Moreover, they suppose that humans collected
foods without the typical adaptations that other mammals use when they
collect the same foods. We have no large digging-claws, for example, we are
slow runners (only some 36 km/hr over short, and some 20 km/hr over long
distances), and we are very prone to dehydration by depletion of water and
salts. We are heavily-built creatures with extensive fat tissues and (in
archaic Homo) heavy bones, features that are not seen in cursorial species.
Our cheekteeth lack the seed-grinding adaptations of baboons, while the
human gastro-intestinal tract and digestive anatomy and physiology are
typical of frugi-omnivores such as suids, not carnivorous mammals (Stevens
1990). This contradiction has been labelled the ?baboon paradox¹, because we
would expect humans to be more similar to baboons if we evolved on the
savannah as they apparently did (Bender 1999).
The collection of waterside food resources, on the other hand, is compatible
with the presumed lifestyle of early apes, and fits with modern human
food-gathering strategies. Shifting from a fruit-based diet to a diet
including more waterside foods such as coconuts and shellfish does not
require significant behavioural modification. The use of tools to open
hard-shelled nuts and fruits is easily transferable so that the meat of
certain molluscs can also be procured (capuchin monkeys use tools to open
fruit, nuts and shellfish), and shellfish, like fruits and nuts, are sessile
food resources that need only be found and gathered, not chased or hunted.
From fruit, shellfish, plant and egg-gathering it is not difficult to
envisage the incorporation of simple hunting of insects, frogs, turtles,
crabs, fish, birds and mammals which abound at the water¹s edge. We do not
claim to know exactly how this waterside lifestyle evolved, but we are
confident that the limited diving skills of humans came about as a result of
increased time spent foraging under water. As to how frequently our
ancestors may have dived or waded or collected fruit from trees or foods
along the shore at low tide, or how long our ancestors¹ waterside phase (or
phases) may have lasted, these are all questions requiring further
investigation.


.

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